Chemotactic behavior ofAeromonas hydrophila

Catalase activity in crude extracts ofEscherichia coli has two pH optima: one at pH 6.8 and the other at pH 10.5. The former is inducible by H₂O₂ and is the major species in exponential cells. The latter is constitutive and is the major species in stationary cells. Both activities are repressed by glucose. Catalase-negative mutants that are impaired in the pH-6.8 activity were isolated by the inability of aerobically grown mutagenized colonies to decompose H₂O₂. One mutant (cat2) characterized is hypersensitive to H₂O₂.